Background/Objectives: Certain aspects of retinal thickness assessed by optical coherence tomography (OCT) in patients with Parkinson’s disease (PD) require additional clarification. It is supposed that attributing reduced retinal thickness in PD to dopaminergic loss may not be acceptable as it also happens in diseases where dopaminergic loss does not occur. The objective of our study is to compare the ganglion cell/inner plexiform layer (GCIPL), peripapillary retinal nerve fiber layer (pRNFL), and macular thickness of PD and dopa responsive dystonia (DRD) patients with healthy controls (HC), to investigate whether DRD patients, as a distinctive model of genetically induced dopamine deficiency, have reduced retinal thickness in comparison with PD, and to analyze correlation between retinal thickness and various PD clinical parameters. Methods: We analyzed 86 patients with PD, 10 patients with DRD, and 96 age- and sex-matched HC. Results: GCIPL, pRNFL, and central macula thickness (CMT) are statistically significantly thinner in PD patients compared to HC (p < 0.001, all). GCIPL and CMT are also statistically significantly thinner in DRD patients compared to HC (p = 0.012, p = 0.001, respectively). GCIPL thickness correlates positively with the daily dose of levodopa (r = 0.244, p < 0.01). The thickness of GCIPL and pRNFL correlate negatively with current age (r = −0.219; p < 0.01 and r = −0.358; p < 0.05, respectively). All retinal parameters are statistically significantly thinner in females than in males (p < 0.05). Conclusions: Patients with PD and DRD did not differ in GCIPL and pRNFL thickness when compared to one another. These results, supported by positive correlation of levodopa dose and GCIPL thickness in PD patients, emphasize the importance of dopamine in maintaining retinal thickness.

Background/Objectives: Clinical differentiation between Parkinson’s disease (PD) and atypical parkinsonism (AP) remains complex. Current diagnostic procedures helpful in their distinction lack specificity, making non-invasive tools like optical coherence tomography (OCT) crucial in evaluating possible retinal changes as potential biomarkers. Our study examined the thickness of the ganglion cell inner plexiform layer complex (GCIPL), peripapillary retinal nerve fiber layer (RNFL) and macular segments in individuals with PD, multiple system atrophy (MSA), progressive supranuclear palsy (PSP), and healthy controls (HC). The objective of our study was to determine if OCT analyses can effectively discriminate PD patients from HC and whether retinal thickness can distinguish typical PD patients from those with AP. Methods: Research was an observational, cross-sectional study. Multiple retinal layers measured with OCT of PD and AP patients were compared with age- and sex-matched HC. An intergroup assessment was conducted. Results: Patients with PD and PSP exhibit a thinner GCIPL compared to HC, with no difference observed in the MSA group. GCIPL thickness between investigational groups does not differentiate between PD and AP. The RNFL and central macula thickness were statistically significantly reduced in all patient groups compared to HC. The RNFL was thinner in PSP compared to PD. Nearly all inner and outer macular segments were thinner in the investigational groups compared to HC. The preservation of outer nasal segments distinguished HC from both typical and AP. Patients with PSP and PD differed in the thickness of all macular segments, being thinner in PSP patients. Conclusions: Thickness of multiple retinal layers and macular regions might serve as a distinguishing feature between PD, AP and HC.